In both Long Term Evolution (LTE) and Wideband Code Division Multiple Access (WCDMA) wireless communication systems, ringing tones can be heard on the downlink at the call-originating user equipment (UE) during the period from when the call is initiated until the called party answers the call. These ringing tones are typically generated in the target Mobile Switching Center (MSC) (e.g., the MSC associated with the called party) and sent back to the call-originating UE through the serving MSC (e.g., the MSC serving the call-originating UE). In the case where the called party is located in the Public Switched Telephone Network (PSTN), the ringing tones may be generated in the PSTN and sent back to the call originating UE.
The ringing tones that are sent back to the call-originating UE, during the period after the call is initiated and prior to the called party answering the call, are transmitted over a traffic channel in the radio network on a downlink to the UE. From an investigation of speech bursts in WCDMA networks, it has been determined that approximately 5% of speech bursts are generated by ringing tones, or about 2% of the downlink activity. Approximately 5% of downlink time consists of ringing tones.
At the generation of the ringing tones when a call is initiated prior to the call being answered, the load on the radio interface in the cell serving the call-originating UE will increase, potentially causing congestion that can disturb other calls in the cell. This added congestion due to the presence of ringing tones in the cell can, in certain instances, force disconnection of established calls. When the ringing tones happen to be coincident for several calls, several forced disconnections can occur at the same time. The presence of ringing tones on the downlink in cells of a wireless communication system may, therefore, have a detrimental impact on service in the cells in certain circumstances.